The present invention relates to an internal combustion engine, with a bypass control system for a supercharger.
2. Description of Related Art
Japanese Unexamined Patent Publication (kokai) No. 56-167817 discloses an internal combustion engine which has an intake passageway including a by-pass. The by-pass by-passes a mechanical supercharger arranged in the intake passageway. A by-pass control valve is arranged in the by-pass and controlled in accordance with the engine load.
The by-pass control valve is adapted to control the amount of air passing through the by-pass when the engine is under supercharging conditions, i.e., when a clutch is engaged to operate the supercharger. The by-pass control valve is closed when the engine load is high, so that a full amount of air is introduced from the supercharger into the engine. When the engine load becomes small, the by-pass control valve is opened, so that part of the air in the intake passageway is diverted into the by-pass, thereby decreasing the amount of air introduced into the engine. This by-pass operation decreases the amount of work expended on compression by the supercharger and, therefore, increases fuel consumption efficiency when the engine is in a partial load condition. The by-pass operation further prevents an increase in the temperature of the intake air when the engine is in a partial load condition. This increase in temperature would otherwise occur if the full amount of air were introduced into the engine without being by-passed during the partial load condition.
The prior art system is disadvantageous because a large noise is created when the engine is abruptly decelerated. This is due to the fact that the supercharger is located upstream from the throttle valve in the intake passageway. When the throttle valve is returned abruptly to the fully closed condition during the deceleration, inertia force is generated in the by-pass, temporarily creating a large flow of air in the by-pass. This generates noise which is transmitted outside without suppression since the throttle valve is located downstream of the supercharger.